3D representation of the Non-Rotating Origin

Olivier de Viron and Veronique DehantRoyal Observatory of Belgium

Scientific adviser:Nicole Capitaine

The Terrestrial Reference Frame

The Celestial Reference Frame

2 systems in an ideal world

The less ideal world

TRF

CRFIntermediateRS

1. polar motion in Earth

2. Earth rotation

3. Celestial motion of CIP

Only the intermediate system is different when using the new or the old formalism. The definition of the TRF and CRF are not affected.

The old-version transformation

1. From TRF to CIP

2. To the True equinox of the date

How to go from one equinox another?

Equator 1

Ecliptic 1

Ecliptic 2

Equator 2

x

Z

y

How to go from one equinox another?

Equator 1

Ecliptic 1

Ecliptic 2

i

Z

rotation 1 (z)

x

y

xy

How to go from one equinox another?

Equator 1

Ecliptic 2

i

x

Z

y

y

Z

Rotation2(x)

How to go from one equinox to another?

Equator 1

Ecliptic 2

i

Z

yx

Rotation4(z)

xEquator 2

How to go from one equinox to another?

Ecliptic 2

Z

xEquator 2

Z

Rotation5(x)

How to go from one equinox another?

Ecliptic 2

xEquator 2

It took 5 successive steps…

True equator ofthe dateMean equator of the date

Equator at J2000

Mean ecliptic of the date

True ecliptic ofthe date

Ecliptic at J2000

v0

12

3 4

The new transformation

1. From TRF to CIP

2. From the terrestrial NRO

3. Earth Rotation Angle

4. To the XCRF projection: s

5. To CRF: celestial motion of the CIP

What is the NRO

2. Not a point in particular, any point of the CIP equator can work.

1. Characterized by its motion: no velocity around the CIP equator associated with polar motion or nutation.

3. Allows to get rid of the equinox in the change of reference frame.

So, we can take any points we want?

2. But, we want the new system to be consistent with the old one.

1. Yes, it is not the point it-self that matter, but its motion.

3. Thus, the point is chosen to insure continuity.

ConclusionsThe NRO is defined by

its position at the base epoch (continuity)

its motion (no motion in the CIP equator associated with polar motion).

Only the Intermediate system is involved, no change of the CRF or TRF